The present invention relates generally to so-called "electronic article surveillance", and in particular, to a system which involves the use of electronically detectable tags or labels which are attached to articles of merchandise in order to protect these articles from unauthorized removal, such as by shoplifting.
For enhanced security and inventory control, the use of electronic article surveillance (EAS) systems has become increasingly widespread. These systems utilize tags or labels which contain an electronic circuit (e.g., a resonant circuit) for interacting with an applied (e.g., swept radio-frequency) electromagnetic field. A transmitter and accompanying antenna produce this field, and a nearby receiver and accompanying antenna detect variations in the received field caused by the presence of a tag. This transmitting and receiving equipment is positioned at the location or locations where it is desired to detect the unauthorized removal of tag-bearing articles, e.g., at the exit of a retail store.
An important consideration in connection with the use of such EAS systems is to minimize the occurrence of false alarms which could either cause embarrassment to customers of the retail store, or produce annoying alarm signals when no one is passing through the store's EAS system. To this end, consideration must be given to what are essentially three different types of false alarm signals, as follows.
For example, an alarm (generally referred to as a "false" alarm) can at times occur when a shopper passes through the EAS system, without possessing any tag-bearing (i.e., protected) merchandise, but an alarm is nevertheless sounded. Yet another, more specific type of false alarm signal is the so-called "merchandise" alarm, which occurs when a shopper carries non-protected merchandise through the EAS system which nevertheless exhibits the characteristics of an active tag or label. Examples of this are items such as extension cords and cables, foldable chairs, and other coiled metal objects which are capable of resonance in the presence of the electromagnetic field of an EAS system. Yet another, more specific type of false alarm signal is the so-called "phantom" alarm, which occurs when an EAS system sounds an alarm responsive to the detection of an "ambient" signal, generally when there is no one passing through the EAS system. Examples of this are false alarm signals produced by tag bearing merchandise placed on display near enough to the EAS system to accidently cause its activation.
Various measures have been taken to reduce false alarms, to the extent possible. One approach which has been attempted in an effort to reduce the occurrence of phantom alarms is to operate the EAS system responsive to an auxiliary sensor which can detect when a shopper is passing through the EAS system. This can be accomplished using any of a variety of available proximity sensors including photoelectric sensors, body heat sensors, floor switches and the like. An example of an EAS system which presently makes use of an auxiliary sensor of this general type is the "Quicksilver" System available from Checkpoint Systems, Inc. of Thorofare, N.J.
In operation, the auxiliary sensor which is provided is used to initiate (activate) operation of the associated EAS system. Thus, it is only upon detecting the presence of a shopper exiting the retail store that the auxiliary sensor will cause activation of the EAS system, so that phantom alarms are effectively eliminated.
However, EAS systems which employ auxiliary sensors of this type do not serve to eliminate false alarms, or merchandise alarms. This is because, once activated (upon detecting the presence of a shopper), the associated EAS system is then operated in entirely conventional fashion to detect the presence of active tags or labels affixed to merchandise being carried by the person passing through the EAS system. Thus, while eliminating the annoyance of phantom alarms, such systems do not eliminate the significant embarrassment of a false alarm or a merchandise-activated alarm. Rather, the EAS system will still be able to produce such false alarm signals. Larger (generally coiled) merchandise will still be able to produce merchandise alarms. Tags or labels attached to merchandise located near the EAS system will still be able to produce false alarms. What is more, the true cause of such false alarm signals then tends to be cloaked by the intermittent operation of the EAS system, which is then activated only when a shopper is present.
Yet another disadvantage which can present itself is that because the EAS system is activated only responsive to the presence of a shopper, care must be taken to provide the EAS system with sufficient time to detect an active tag or label (i.e., a complete acquisition cycle must occur). Depending upon the manner in which the tag or label is oriented with respect to the EAS system, and the speed at which the tag or label is being carried through the EAS system, the potential exists for protected merchandise to be missed by the EAS system. In essence, the protected merchandise is permitted to pass through the EAS system before the EAS system has had sufficient time to respond to the associated tag or label.
As a result of the foregoing, EAS systems which are activated responsive to auxiliary sensors have enjoyed only sporadic use. It therefore became desirable to improve upon such systems to enhance their reliability, and accordingly, their attractiveness to retail stores.